1. Field of the Invention
The present invention relates to a continuous and discontinuous process for preparing cyclic butadiene trimers, i.e. cyclododeca-1,5,9-triene (CDT) using a catalyst system containing nickel and/or titanium. Furthermore, the present invention relates to the abovementioned process in which cyclooctadiene (COD) and/or vinylcyclohexene (VCH) can additionally be isolated from the reaction mixture, preference being given to using a nickel-containing catalyst system in this case. The present invention also encompasses mixtures having a particular ratio of CDT to C16-, C20-, C24-hydrocarbons and polymers having molecular weights up to 5000. It further encompasses mixtures having CDT as main constituent and a very small proportion of chlorocyclododecatriene (Cl-CDT). These mixtures can be obtained by the process of the invention.
2. Description of Related Art
A large number of patents and publications are concerned with processes or experiments for preparing cyclic dimers and trimers of conjugated dienes, in particular butadiene.
The formation of cyclododecatriene in the presence of a titanium catalyst has been described, for example, in JP-A-2003064011. Here, the reaction was carried out using a catalyst system composed of titanium tetrachloride, 4,4′-dichlorobenzophenone, dimethyl sulfoxide and diethylaluminum sesquichloride at a temperature of 40° C. After the reaction was complete, the mixture was admixed with MeONa/MeOH and washed with aqueous trisodium citrate to remove the titanium and aluminum from the organic reaction mixture. JP-A-02083339 describes a similar process, likewise using DMSO. The presence of the high-boiling DMSO as additive is disadvantageous for an industrial process since it has to be removed again from the reaction mixture.
FR-A-1393071 describes the formation of CDT using titanium and aluminum as catalyst system. As titanium catalyst, use was made of Ti(OR)4, where R is an aliphatic C3-C4-alkyl radical, and AlR′X2 or AlRK′2X, where R′ is a straight-chain or branched C1-C18-alkyl radical or a C1-C6-cycloalkyl radical or a C1-C10-aralkyl radical and X is Cl or Br, was used as aluminum catalyst. The reaction described in FR1393071 requires very long reaction times of 18 hours and is therefore unsuitable for industrial use. Furthermore, no yields are reported in the French patent.
U.S. Pat. No. 3,499,049 describes a method of accelerating the catalytic trimerization of butadiene by addition of water to the reaction mixture. This process has the disadvantage that the amount of undesirable by-products is too high. Particularly in continuous operation, the yields of CDT of 83% or 62% achieved in U.S. Pat. No. 3,499,049 are not sufficient for industrial use.
GB 928,812 likewise describes a process for preparing cyclododecatriene using specific catalysts containing a semipolar double bond in the molecule. The best results are achieved using DMSO, which as indicated above leads to disadvantages in the work-up of the reaction mixture.
DE 1140569 discloses the formation of dimers and trimers of 1,3-diolefins by means of nickel or cobalt catalyst systems. The catalyst systems additionally contain organometallic compounds and compounds having electron donor properties. The process of DE 11 40 569 requires the use of dry solvents, which is associated with a considerable technical outlay and thus economic disadvantages.
In the industrial trimerization of butadiene to cyclododecatriene (CDT), homogeneous catalysts are used and the reaction is carried out in a continuous process in one or more stirred vessels. Parts of the reaction mixture are taken off continuously from the reaction mixture. During the work-up, unreacted starting material is recovered and is returned together with fresh butadiene to the circuit. When parts of the reaction mixture are taken off, parts of the catalyst are likewise taken from the reaction mixture. As a result, the concentration of the catalyst in the reaction mixture drops and the catalyst taken off has to be replaced by fresh catalyst in order to keep the catalyst concentration constant.
Before the work-up of the material taken off from the reactor, the catalyst taken off has to be destroyed. Many polar solvents are used for this purpose. Apart from water, Ube Industries utilizes, for example, ammonium hydroxide solutions (JP-A-05-070377, JP 06-25438). Various alcohols can likewise be utilized (JP-A-07-625439, JP 07-625396). In particular, methanol (JP-A-07-442496) and methanol/HCl (DE-A-19 42 729) are preferably used.
The decomposition of the catalyst can also be carried out by means of acetone (JP-A-04-301345) or by means of a suspension of calcium oxide in water NL-A-6 603 264). Ube Industries has additionally reported that the yield of CDT drops when water is used to decompose the catalyst.